Field of the Invention
The present invention relates to an oxide superconductor wire and a method of manufacturing an oxide superconductor wire.
Description of the Related Art
A RE-123-based oxide superconductor (REBa2Cu3O7−X: RE represents a rare earth element containing Y) exhibits superconductivity at a liquid nitrogen temperature. Since the RE-123-based oxide superconductor has low current loss, this RE-123-based oxide superconductor is processed into a superconductor wire to manufacture a superconductor or a superconducting coil for supplying power. As a method of processing this oxide superconductor into a wire, a method may be used, the method including: forming an oxide superconductor layer over a substrate as a metal tape with an intermediate layer interposed therebetween; and forming a stabilizing layer on the oxide superconductor layer.
A commonly-used oxide superconductor wire of the related art adopts a structure in which two stabilizing layers are laminated, the two stabilizing layers including: a thin silver stabilizing layer that is formed on an oxide superconductor layer; and a thick stabilizing layer that is formed on the thin silver stabilizing layer using a highly conductive metal material such as copper. The silver stabilizing layer is also provided for adjusting changes in oxygen content during an oxygen heat treatment of the oxide superconductor layer. The copper stabilizing layer functions as a bypass for commutating a current of the oxide superconductor layer when the oxide superconductor layer is transitioned from the superconducting state to the normal conducting state.
In addition, a RE-123-based oxide superconductor having a specific composition is likely to deteriorate due to moisture. Therefore, in a case where a superconductor wire is stored in an environment containing a large amount of moisture or where a superconductor wire is left to stand in a state where moisture is attached thereon, when moisture is infiltrated into the oxide superconductor layer, there is a concern that superconductivity may deteriorate. Accordingly, in order to secure long-term reliability of a superconductor wire, it is necessary that a structure for protecting the entire periphery of a superconductor layer with a layer be adopted.
As a structure of the related art for protecting the entire periphery of a superconductor layer, as in the case of a high-temperature superconductor wire disclosed in Published Japanese Translation No. 2009-503794 of the PCT International Publication, a structure including: a laminated structure in which two superconductor insert layers are laminated; and a nonporous electrically conductive filler such as solder which covers the laminated structure, is known. In addition, this high-temperature superconductor wire has a configuration in which both sides or four peripheries of the above-described laminate are surrounded by a metal stabilizer strip, and the inside of the stabilizer strip is filled with the nonporous electrically conductive filler.
In addition, as in the case of a reinforced high-temperature superconductor wire disclosed in Japanese Unexamined Patent Application, First Publication No. 2011-003494 including a tape-shaped oxide superconductor as a reinforcement structure, a structure including a tape-shaped high-temperature superconductor wire in which an intermediate layer and an oxide superconductor layer are laminated on a metal substrate is known, in which the high-temperature superconductor wire is covered with a C-shaped reinforcement tape wire both ends of which are bent, and at least a part of the high-temperature superconductor wire is soldered to the reinforcement tape wire.
In a superconductor wire including the above-described RE-123-based oxide superconductor layer, an oxide superconductor layer is laminated over a metal tape as a substrate with an intermediate layer interposed therebetween, and a thin silver stabilizing layer is laminated on the oxide superconductor layer. However, since this thin silver stabilizing layer is formed thin so as to adjust changes in oxygen content during a oxygen heat treatment, pin holes may be present thereon. In addition, the silver stabilizing layer is formed using a film forming method such as a sputtering method. Therefore, when a long superconductor wire is manufactured, there is a problem in that peeling, chipping, or the like is likely to occur. Further, a surface of the oxide superconductor layer is covered with the silver stabilizing layer, but side surfaces of the oxide superconductor layer are not covered with a layer. Accordingly, it is necessary that a countermeasure against moisture infiltration from the side surfaces be taken.
To that end, as disclosed in the above-described Patent documents, the structure in which the superconductor insert layers of the laminate structure are surrounded by the metal stabilizer strip or the structure in which the high-temperature superconductor wire is surrounded by the C-shaped reinforcement tape is considered to be effective. However, a structure in which a tape-shaped oxide superconductor is surrounded by a metal tape or the like and is fixed thereto through a solder has a problem in solder adhesion at an interface between a copper tape and an oxide superconductor. In addition, when even a small gap is formed in the entire periphery of a long superconductor wire, moisture may be infiltrated into the superconductor wire through the gap.
FIG. 8 illustrates an example of a structure which is made assuming that such an oxide superconductor is surrounded by a copper tape. In the structure illustrated in FIG. 8, a tape-shaped oxide superconductor laminate 104 is formed by laminating an oxide superconductor layer 102 and a silver stabilizing layer 103 over one surface of a metal tape-shaped substrate 100 with an intermediate layer 101 interposed therebetween. Further, an oxide superconductor 106 having a coating structure is formed by surrounding the periphery of the oxide superconductor laminate 104 with a copper tape 105. In the oxide superconductor 106 of this example, for example, a solder layer 107 is formed at an end portion of the copper tape 105. In addition, on a back surface of the substrate 100, end portions of the copper tape 105 are made to overlap each other and are soldered to each other such that the end portions of the copper tape 105 are integrated.
On the other hand, in the structure illustrated in FIG. 8 in which the oxide superconductor laminate 104 is surrounded by the copper tape 105, when overlapping portions of the copper tape 105 are soldered to each other, and when there are even a small amount of defects in solder joints over the entire periphery of the tape-shaped oxide superconductor laminate 104, moisture may be infiltrated thereinto, and moisture infiltration cannot be completely prevented.
In addition, in the oxide superconductor 106 having the structure of FIG. 8, the thickness of a portion of the copper tape 105 where one end overlaps the other end significantly varies. Accordingly, when the superconductor 106 is wound around a winding barrel to form a superconductive coil or the like, there is no problem in the case of one-layer winding, but there is a problem of irregular winding at an overlapping portion of the copper tape 105 in the case of multi-layer winding.
The present invention has been made in consideration of the above-described circumstances of the related art, and an object thereof is to provide an oxide superconductor wire in which a structure capable of preventing moisture infiltration is formed for an oxide superconductor layer inside the structure not to deteriorate. In addition, another object of the present invention is to provide an oxide superconductor wire in which irregular winding does not occur when the oxide superconductor wire is wound in a coil shape to form a superconductive coil or the like.